The present invention relates to a method for manufacturing a sintered piece, and in particular, to a method for manufacturing a sintered piece including calcium phosphate compound.
Hydroxyapatite is a kind of calcium phosphate ceramics (calcium phosphate compound) and is a main constituent of bones and tooth. Thus, hydroxyapatite is used as biomaterial for an artificial bone, an artificial dental root, and medical/dental cement, for example. That is, hydroxyapatite is shaped to a desired form by means of molding, and then baked to obtain a sintered piece of hydroxyapatite which is usable as the artificial bone or dental root.
When it is used as the artificial bone or dental root, the sintered piece of the hydroxyapatite is required to have both high mechanical strength and good bio-compatibility. The mechanical strength of the sintered piece can be enhanced by increasing the relative density thereof. However, the bio-compatibility of the sintered piece decreases with the increase of the relative density of the sintered piece, and vice versa, since the growth of the osteoblast into the sintered piece becomes more difficult with the increase of the relative density thereof.
Therefore, there was a demand for a method for increasing the mechanical strength of the sintered piece of hydroxyapatite without increasing its relative density.
The present invention is advantageous in that it provides a method for manufacturing a sintered piece including calcium phosphate compound and has high mechanical strength but low relative density.
According to an aspect of the invention, there is provided a method for manufacturing a sintered piece in which a molded piece of a composite including calcium phosphate compound such as hydroxyapatite is prepared and then baked in an oxygen atmosphere to obtain the sintered piece. The oxygen concentration of the oxygen atmosphere is controlled to be not less than 25 vol %. Optionally, the relative humidity of the oxygen atmosphere is controlled to be below 30% RH. The baking is performed for 30 minutes to 8 hours at a temperature not less than 1000xc2x0 C. but below a temperature at which thermal decomposition of the calcium phosphate occurs. The sintered piece obtained as above has high mechanical strength with low relative density thereof.
Optionally, at least a part of the molded piece is covered with a sinter assisting material, during the baking, that enables efficient heating of the covered part of the molded piece to increase the mechanical strength thereof. It is found that powder, in particular that having average particle diameters of 3 to 300 xcexcm, is suitable for the sinter assisting material since such powder allows the gas surrounding the molded piece to be exchanged and in turn the atmosphere around the molded piece to be uniform.
A material of which main component is calcium phosphate compound is suitable for the sinter assisting material since the bio-compatibility of the sintered piece will not be affected even if such a sinter assisting material has contaminated or adhered to the sintered piece. The sinter assisting material is preferably pre-baked in advance of the baking of the molded piece at a temperature not less than the temperature of the baking to deactivate the sinter assisting material.
Optionally, the molded piece is pre-baked in advance of the baking, or main baking. The pre-baking may be performed under different condition from that of the main baking of the molded piece. For example, the pre-baking may be performed in air atmosphere to reduce the manufacturing cost of the sintered piece.